The present invention relates to fuel delivery in an internal combustion engine.
Since the 1970xe2x80x2s, port-fuel injected engines have utilized three-way catalysts and closed-loop engine controls in order to seek to minimize NOx, CO, and unburned hydrocarbon emissions. This strategy has proven to be particularly effective during normal operation in which the engine and exhaust components have reached sufficient temperatures. However, in order to achieve desirable conversion efficiencies of NOx, CO, and unburned hydrocarbons, the three-way catalyst must be above its inherent catalyst light-off temperature.
In addition, the engine must be at sufficient temperature to allow for vaporization of liquid fuel as it impinges upon intake components, such as port walls and/or the back of valves. The effectiveness of this process is important in that it provides a proper degree of control over the stoichiometry of the fuel/air mixture and, thus, is coupled to idle quality and the performance of the three-way catalyst, and it ensures that the fuel supplied to the engine is burned during combustion and, thus, eliminates the need for over-fueling to compensate for liquid fuel that does not vaporize sufficiently and/or collects on intake components.
In order for combustion to be chemically complete, the fuel-air mixture must be vaporized to a stoichiometric gas-phase mixture. A stoichiometric combustible mixture contains the exact quantities of air (oxygen) and fuel required for complete combustion. For gasoline, this air-to-fuel ratio is about 14.7:1 by weight. A fuel-air mixture that is not completely vaporized, and/or contains more than a stoichiometric amount of fuel, results in incomplete combustion and reduced thermal efficiency. The products of an ideal combustion process are water (H2O) and carbon dioxide (CO2). If combustion is incomplete, some carbon is not fully oxidized, yielding carbon monoxide (CO) and unburned hydrocarbons (HC).
Under cold-start and warm-up conditions, the processes used to reduce exhaust emissions and deliver high quality fuel vapor break down due to relatively cool temperatures. In particular, the effectiveness of three-way catalysts is not significant below approximately 250xc2x0 C. and, consequently, a large fraction of unburned hydrocarbons pass unconverted to the environment. Under these conditions, the increase in hydrocarbon emissions is exacerbated by over-fueling required during cold-start and warm-up. That is, since fuel is not readily vaporized through impingement on cold intake manifold components, over-fueling is necessary to create combustible mixtures for engine starting and acceptable idle quality.
The mandates to reduce air pollution worldwide have resulted in attempts to compensate for combustion inefficiencies with a multiplicity of fuel system and engine modifications. As evidenced by the prior art relating to fuel preparation and delivery systems, much effort has been directed to reducing liquid fuel droplet size, increasing system turbulence and providing sufficient heat to vaporize fuels to permit more complete combustion.
However, inefficient fuel preparation at lower engine temperatures remains a problem which results in higher emissions, requiring after-treatment and complex control strategies. Such control strategies can include exhaust gas recirculation, variable valve timing, retarded ignition timing, reduced compression ratios, the use of catalytic converters and air injection to oxidize unburned hydrocarbons and produce an exothermic reaction benefiting catalytic converter light-off.
As indicated, over-fueling the engine during cold-start and warm-up is a significant source of unburned hydrocarbon emissions in conventional engines. It has been estimated that as much as 80 percent of the total hydrocarbon emissions produced by a typical, modern port fuel injected (PFI) gasoline engine passenger car occurs during the cold-start- and warm-up period, in which the engine is over-fueled and the catalytic converter is essentially inactive.
Given the relatively large proportion of unburned hydrocarbons emitted during startup, this aspect of passenger car engine operation has been the focus of significant technology development efforts. Furthermore, as increasingly stringent emissions standards are enacted into legislation and consumers remain sensitive to pricing and performance, these development efforts will continue to be paramount. Such efforts to reduce start-up emissions from conventional engines generally fall into two categories: 1) reducing the warm-up time for three-way catalyst systems and 2) improving techniques for fuel vaporization. Efforts to reduce the warm-up time for three-way catalysts to date have included: retarding the ignition timing to elevate the exhaust temperature; opening the exhaust valves prematurely; electrically heating the catalyst; burner or flame heating the catalyst; and catalytically heating the catalyst. As a whole, these efforts are costly and do not address HC emissions during and immediately after cold start.
A variety of techniques have been proposed to address the issue of fuel vaporization. U.S. patents proposing fuel vaporization techniques include U.S. Pat. No. 5,195,477 issued to Hudson, Jr. et al, U.S. Pat. No. 5,331,937 issued to Clarke, U.S. Pat. No. 4,886,032 issued to Asmus, U.S. Pat. No. 4,955,351 issued to Lewis et al., U.S. Pat. No. 4,458,655 issued to Oza, U.S. Pat. No. 6,189,518 issued to Cooke, U.S. Pat. No. 5,482,023 issued to Hunt, U.S. Pat. No. 6,109,247 issued to Hunt, U.S. Pat. No. 6,067,970 issued to Awarzamani et al., U.S. Pat. No. 5,947,091 issued to Krohn et al., U.S. Pat. No. 5,758,826 issued to Nines, U.S. Pat. No. 5,836,289 issued to Thring, and U.S. Pat. No. 5,813,388 issued to Cikanek, Jr. et al.
Other fuel delivery devices proposed include U.S. Pat. No. 3,716,416, which discloses a fuel-metering device for use in a fuel cell system. The fuel cell system is intended to be self-regulating, producing power at a predetermined level. The proposed fuel metering system includes a capillary flow control device for throttling the fuel flow in response to the power output of the fuel cell, rather than to provide improved fuel preparation for subsequent combustion. Instead, the fuel is intended to be fed to a fuel reformer for conversion to H2 and then fed to a fuel cell. In a preferred embodiment, the capillary tubes are made of metal and the capillary itself is used as a resistor, which is in electrical contact with the power output of the fuel cell. Because the flow resistance of a vapor is greater than that of a liquid, the flow is throttled as the power output increases. The fuels suggested for use include any fluid that is easily transformed from a liquid to a vapor phase by applying heat and flows freely through a capillary. Vaporization appears to be achieved in the manner that vapor lock occurs in automotive engines.
U.S. Pat. No. 6,276,347 proposes a supercritical or near-supercritical atomizer and method for achieving atomization or vaporization of a liquid. The supercritical atomizer of U.S. Pat. No. 6,276,347 is said to enable the use of heavy fuels to fire small, light weight, low compression ratio, spark-ignition piston engines that typically burn gasoline. The atomizer is intended to create a spray of fine droplets from liquid, or liquid-like fuels, by moving the fuels toward their supercritical temperature and releasing the fuels into a region of lower pressure on the gas stability field in the phase diagram associated with the fuels, causing a fine atomization or vaporization of the fuel. Utility is disclosed for applications such as combustion engines, scientific equipment, chemical processing, waste disposal control, cleaning, etching, insect control, surface modification, humidification and vaporization.
To minimize decomposition, U.S. Pat. No. 6,276,347 proposes keeping the fuel below the supercritical temperature until passing the distal end of a restrictor for atomization. For certain applications, heating just the tip of the restrictor is desired to minimize the potential for chemical reactions or precipitations. This is said to reduce problems associated with impurities, reactants or materials in the fuel stream which otherwise tend to be driven out of solution, clogging lines and filters. Working at or near supercritical pressure suggests that the fuel supply system operate in the range of 300 to 800 psig. While the use of supercritical pressures and temperatures might reduce clogging of the atomizer, it appears to require the use of a relatively more expensive fuel pump, as well as fuel lines, fittings and the like that are capable of operating at these elevated pressures.
One object is to provide a fuel injector having improved fuel vaporization characteristics under all engine operating conditions, particularly cold-start and warm-up conditions.
Another object is to provide a fuel injector and delivery system capable of reducing emissions.
It is a further object to provide a fuel injector and delivery system that can supply vaporized fuel while requiring minimal power and warm-up time, without the need for a high pressure fuel supply system, which may be utilized in a number of configurations including conventional port-fuel injection, hybrid-electric, gasoline direct-injection, and alcohol-fueled engines.
These and other objects will become apparent from the detailed description of the preferred forms set out below and now summarized as follows:
A preferred form of the fuel injector for vaporizing a liquid fuel for use in an internal combustion engine is intended to accomplish at least one or more of the aforementioned objects. One such form includes at least one capillary flow passage, said at least one capillary flow passage having an inlet end and at least one outlet end; a heat source arranged along said at least one capillary flow passage, said heat source operable to heat the liquid fuel in said at least one capillary flow passage to a level sufficient to change at least a portion thereof from the liquid state to a vapor state and deliver a stream of substantially vaporized fuel from said outlet end of said at least one capillary flow passage; and a valve for metering fuel to the internal combustion engine, said valve located proximate to said outlet end of said at least one capillary flow passage, said valve including a low mass member for substantially occluding the stream of fuel to the internal combustion engine; wherein said low mass member for substantially occluding the stream of fuel to the internal combustion engine is formed of a material having low mass and/or a low coefficient of thermal conductivity. The fuel injector is effective in reducing cold-start and warm-up emissions of an internal combustion engine. Efficient combustion is promoted by forming an aerosol of fine droplet size when the substantially vaporized fuel condenses in air. The vaporized fuel can be supplied directly or indirectly to a combustion chamber of an internal combustion engine during cold-start and warm-up of the engine, or at other periods during the operation of the engine, and reduced emissions can be achieved due to capacity for improved mixture control during cold-start, warm-up and transient operation.
One preferred form also provides a method of delivering fuel to an internal combustion engine. The method includes the steps of supplying liquid fuel to at least one capillary flow passage of a fuel injector; causing a stream of substantially vaporized fuel to pass through an outlet of the at least one capillary flow passage by heating the liquid fuel in the at least one capillary flow passage; and metering the vaporized fuel to a combustion chamber of the internal combustion engine through a valve located proximate to the outlet end of the at least one capillary flow passage, the valve including a low mass member for substantially occluding the stream of fuel to the internal combustion engine, wherein the low mass member for substantially occluding the stream of fuel to the internal combustion engine is formed of a material having a low mass and/or low coefficient of thermal conductivity.
Another preferred form provides a fuel system for use in an internal combustion engine, the fuel system including a plurality of fuel injectors, each injector including at least one capillary flow passage said at least one capillary flow passage having an inlet end and an outlet end; a heat source arranged along the at least one capillary flow passage, said heat source operable to heat the liquid fuel in said at least one capillary flow passage to a level sufficient to change at least a portion thereof from the liquid state to a vapor state and deliver a stream of substantially vaporized fuel from said outlet end of said at least one capillary flow passage; a valve for metering fuel to the internal combustion engine, said valve located proximate to said outlet end of said at least one capillary flow passage, said valve including a low mass member for substantially occluding the stream of fuel to the internal combustion engine; wherein said low mass member for substantially occluding the stream of fuel to the internal combustion engine is formed of a material having a low mass and/or a coefficient of thermal conductivity; a liquid fuel supply system in fluid communication with said plurality of fuel injectors; and a controller to control the supply of fuel to said plurality of fuel injectors.
According to one preferred form, the capillary flow passage can include a capillary tube and the heat source can include a resistance heating element or a section of the tube heated by passing electrical current therethrough. The fuel supply can be arranged to deliver pressurized or non-pressurized liquid fuel to the flow passage. The apparatus can provide a stream of vaporized fuel that mixes with air and forms an aerosol having a mean droplet size of 25 xcexcm or less.
In another preferred form, the means for cleaning deposits includes an oxidizer control valve for placing the at least one capillary flow passage in fluid communication with an oxidizer, the heat source being operable to heat the oxidizer in the at least one capillary flow passage to a level sufficient to oxidize deposits formed during the heating of the liquid fuel. In this embodiment, the oxidizer control valve is operable to alternate between the introduction of liquid fuel and the introduction of oxidizer into the capillary flow passage and enable in-situ cleaning of the capillary flow passage when the oxidizer is introduced into the at least one capillary flow passage. The oxidizer is preferably selected from the group of air, exhaust gas, steam and mixtures thereof.
In another preferred form, the means for cleaning deposits can include a solvent control valve for placing the at least one capillary flow passage in fluid communication with a solvent. In this preferred form, the solvent control valve alternates between the introduction of liquid fuel and the introduction of solvent into the capillary flow passage and enables in-situ cleaning of the capillary flow passage when the solvent is introduced into the at least one capillary flow passage.